It is the object of the present invention to provide a new solar concentrator of simple construction, easy to operate and almost free of maintenance.
The system is adaptable to multiple use, such as solar thermal power plants, solar concentrators for collecting photovoltaic panels, solar heaters for industrial process, etc.
Solar thermal technology concentrates the sun's radiation using tracking mirrors onto a receiver where the solar energy is absorbed as heat and converted into electricity or incorporated into products as process heat. There are two primary solar thermal technologies: central receiver systems and linear receiver systems.
Current central receiver systems use fields of heliostats (two-axis tracking mirrors) to focus the sun's radiant energy onto a central receiver. The field of heliostats is the single most expensive part of such plants. Recent technologies have focused on the development of heliostats that use stretched-membrane reflectors in place of the more familiar glass mirrors. In such heliostats, the metal foils are stretched over both sides of a long-diameter metal ring. The reflector surface is a silvered-polymer film glued to the metal membrane.
The basic concept for the stretched-membrane mirror's design is that a metal foil, when placed in uniform tension, provides an excellent substrate for an optically reflective surface.
The present invention relates to the linear receiver technology, where line focus tracking reflectors concentrate sunlight onto receiver tubes or panels along their focus line. The linear focus allows to track the apparent movement of the sun with only one degree of freedom.
The reflectors are made of metal foils with a reflective surface, stressed in uniform tension. Each metal foil performs as a whole solar mirror, avoiding in this way longitudinal welding to each other.
There are some U.S. Patents, such as U.S. Pat. Nos. 4,293,192, 4,510,923, 4,316,448 and 4,173,397 that also show a variety of concentrator devices with flexible foils of a reflective material, tensioned by mechanical tensioning means. These patents include the use of frame structures that support the tensile stress of said flexible foils.
Generally, such frame structures would be expensive to fabricate, heavy and difficult to employ. For example, it is known that a metal foil must be placed in uniform, high tensile stress for providing a good optically reflective surface (i.e. 13,000 psi for stretched-membrane heliostats tested at Sandia National Laboratories); consequently, it can be appreciated that such support frames include a plurality of heavy and bulky support members in the direction in which the foil is stressed.
A heavy support structure practically offsets the apparent advantage of using metal foil mirrors. The fundamental objective of the present invention is directed to avoid the use of such longitudinal support structures for supporting the tensile stress of the metal foils.
The concentrator employs a plurality of small individual support structures, transverse to the longitudinal direction of the metal foils. Set in arrays, long metal foils with a reflective surface are longitudinally tensioned from both free ends by a pair of end support structures with tensioning means, and supported by a plurality of uniformly spaced intermediate support structures with sliding means.
The construction and assemble of the concentrator system allows for substantial economies of scale. Large reflective surfaces can be supported and driven by a plurality of identical support structures, without mechanical connection to one another.